These bottles will hold at least 120 PSI (8 bar) of pressure. I've only launched it at 6 bar due to lack of an adequate pump (and I don't have a remote launcher yet - see below), but even at that I have trouble finding a park big enough to be safe - an Australian football field is huge by the standards of other football codes, but isn't big enough if the rocket is even slightly unstable at launch - I've had to walk a long way to retrieve it sometimes!

See also Mal Goris's pages, where he describes his development of my launcher with detailed photos and diagrams.

• The nozzle
  I use a plastic garden-hose connector for the nozzle. Cutting it down to the right size and fitting it into the original cap of the bottle is tricky, but works well.

  I use a 19mm spade drill with two teeth on the outer edge to drill a hole in the centre of the bottle top. Most of the hose attachment must be cut away to leave a thin lip only 2mm wide to fit inside the bottle top. Inside that you can use the soft plastic sealer (with the centre cut out) as a washer. I usually glue the nozzle into the bottle top, but that just stops them getting separated, it isn't enough to stop it leaking.

• The fin
  Because the water is expelled more slowly than with an open-mouth launcher, during the early phase of the flight the bottle would be very unstable, since the weight is in the back (rockets need their weight concentrated forward of the centre of pressure). All my experiments with three fins failed until I came up with the cylindrical fin shown in the pictures here.

  Note how far the fin trails behind the rocket - this is essential.

• The launcher
  Use of the hose connector as a nozzle immediately suggests the use of the matching part to pressurise and release the rocket. The launcher shown has a comfortable pistol grip, string-pull trigger, and consists of a piece of plastic hose joined using a hose clamp to a copper pipe with a 90 degree angle piece on the end, joined to a 1/4 inch tube for attachment of an air pump.

  The trigger string is a piece of blind cord, tied around the hose-end tightly and overlapped so as to get the two loose ends to come out on opposite sides, as shown below. You can remember some of that boy-scout stuff, can't you? I passed the string through a plastic cap attached to the copper pipe to stop the ends disappearing to where I can't reach them, and attached a loop for a trigger.

• The nose cone
  The bottom of the bottle has the top of another taped to it to act as a nose cone, and to prevent the hard landings from weakening the high-pressure part. I have had a bottle explode after twenty landings - huge bang - louder than a shotgun! I heard later the local police were called to investigate... Don't hold the bottle while pumping! There was a report during the 1997 test cricket series in South Africa of someone having three fingers sewn back on after a dry-ice bottle grenade blew up while they were holding it. Apparently the grenade (a capped bottle with some dry ice inside) was being thrown around when someone got unlucky. However, the plastic doesn't fragment - just tears open and turns inside-out.

• New nose cones!
  See also the New nose cones of my Guppy rockets.

Closeups of launcher